1. Field of the Invention
The invention relates to a cage for undersea tethered vehicles, and more particularly to a cage having means for winding and storing the tether line.
Typically, the cage with the tethered vehicle therein is lowered into the water, and the vehicle is permitted to leave the cage with the tether line attached.
The tether must be paid out from, and reeled into the cage as the vehicle alternately departs and returns. The tether is typically several hundred feet long and slightly buoyant. The tether is thus vulnerable to entanglement on submerged objects which is a serious problem, inasmuch as tethered vehicles are normally used in proximity to underwater structures and often encounter strong underwater currents and restricted visibility. To minimize the likelihood of entanglement, it is desirable to be able to accurately control the length of tether that is paid out, and to keep this length free of twists.
2. Prior Art
Conventional rotating drum winches will reel cable in and out without imparting a twist do it. However, a rotating drum winch will not reel out satisfactorily unless an external tension is applied to the cable. Another disadvantage is that it is difficult and unreliable to wind cable smoothly onto a rotating drum in the confined space available in a vehicle cage. Still another disadvantage is that a system of terminals and slip rings must be used to transmit electrical signals from the tether on the rotating drum to the stationary transmission cable that leads back to the control station at the surface of the water. For these reasons prior art devices typically store the tether in a stationary drum. However, these devices produce a twist in the tether each time a loop is reeled into the drum. If the twist is absorbed by the length of tether in the drum, it will tend to cause adjacent loops to entangle. If the twist is absorbed by the length of tether outside the drum it will tend to cause the tether to become entangled with other objects in the water, including the cage and vehicle. It will also tend to damage the tether when the twisted length of tether is subsequently drawn into the drum, particularly when several twists are crowded close to one another as the vehicle approaches the cage.
One prior art device includes a cage which, in effect, rests on top of the underwater vehicle and stores only the tether. The tether includes a plurality of beads along the outside of the tether line. The beads operate in conjunction with the cog or toothed wheel on the cage to reel in and play out the tether. The cage only stores the tether, and the storing occurs in a generally loose manner in the cage with no specific orientation of the tether, except generally in a circular manner. The disadvantages of this system are the generally loose storing of the tether line in the cage, a complex tether line, and the extra bulk involved.
Another system involves a vehicle on a tether and a generally cylindrical cage which receives the vehicle therein. The cage is lowered by means of a winch from the deck of a ship. The cage and tether reeling and unreeling mechanism include a bale which rotates within the cage to reel and unreel the tether. It is believed that the tether line is positioned generally loosely in a circular manner in the cage, and the blade exerts a tension on the tether for the purpose of preventing the tether from snarling in the storage area of the cage. One disadvantage of this device is in the generally irregular positioning of the tether line in the cage.
In the prior art, when the tether is wound in a circular manner, for example in a cage, with or without the use of a bale, there is a tendency for the cable to twist and for some of the twists to accumulate in the length of tether between the cage and the vehicle when the tether is paid out of the cage, unless some other device is used or action taken. This causes a problem in reeling in the tether because all of the twists will be concentrated in the last 50 feet or so of the line adjacent the vehicle. Thus, in order to reel the entire tether line into the cage, without damaging it, the vehicle must maneuver around to remove the twist out of the tether, which is time-consuming and difficult to do with certainty.